In past LCD projectors and other image display apparatuses, the size of a pixel (pixel pitch) in the LCD panel or other image display device was usually 10 odd μm or more. In recent years, however, progress has been made in reducing the size and increasing the definition of LCD panels and ones with pixel pitches of 10 μm or less have started to appear in the market.
Along with increasing fineness of pixel pitch, the following problems have been encountered.
The first problem is that a beam of light striking the LCD panel is diffracted by the pixel periodic structure and generates unnecessary high-order diffracted light, particularly “1st order diffracted light with a non-negligible reduction of diffraction efficiency. This not only becomes a cause of stray light (flare) in an LCD projector, but also reduces the luminance, since an amount of 0th order light (non-diffracted light) inherently required is decreased and leads to a reduction in the luminance.
The second problem is the drop in the area ratio of the region through which light can pass to the area of a pixel as a whole, that is, the drop in the aperture ratio. A pixel is formed not only by the pixel electrode forming the aperture, but also a thin film transistor or other switching device and a holding capacitor. As the pixel pitch becomes finer, the area occupied by the switching device and holding capacitor increases relatively. The area of the aperture is sacrificed (becomes smaller) by that amount and a decline in the aperture ratio is caused.
The first problem will be explained. Even in a conventional 10 odd μm pitch LCD panel, in theory, diffracted light occurred due to the pixel periodic structure. Expressing the diffraction phenomenon by an equation, Sin(θ)=(λ/p) is obtained. Here, λ represents the wavelength, p the pixel pitch, and θ the diffraction angle. In the past, the pixel pitch was large, so the diffraction angle θ given by the above equation was small and the 0th order light and high-order diffracted light (“1st order, “2nd order light) were not separated much at all, so the above problem did not conspicuously appear. However, due to the increasing fineness of pixel pitch in recent years, the diffraction angle θ given by the above equation has become large and the above problem can no longer be ignored. This problem is, for example, explained in David Armitage, “Resolution issues in reflective microdisplays”, SPIE, vol. 3634, 10 (1999).
Next, the second problem will be explained. In this type of image display device, in particular a projection type image display device, the circuit pattern of the switching device and holding capacitor for modulating a light beam passing through each pixel is located adjacent to the pixel electrode. Along with the increasing fineness of pixel pitch, however, the ratio of area occupied by the circuit pattern increases. As a result, the problem arises that the aperture ratio falls and the efficiency of utilization of light falls. As a means for solving this problem, the method of providing a micro-lens array comprised of a large number of micro-lenses arranged at the incidence sides of the pixels and using the micro-lens array to focus the light beams striking the pixels is disclosed in for example Japanese Unexamined Patent Publication (Kokai) No. 3-236987. However, the micro-lenses are arranged corresponding to the pixels. Therefore, the micro-lens array itself has a periodic structure similar to the pixel array and diffracted light again arose. This has become a problem even more non-negligible when superposed with the diffraction due to the pixel periodic structure.